A fuel cell system is a system in which a material containing an organic compound composed of at least carbon and hydrogen, such as city gas and LPG, is subjected to a steam-reforming reaction to generate hydrogen-containing gas in a hydrogen generating apparatus having a reforming section therein and the generated hydrogen-containing gas is supplied to a fuel cell to generate power.
The material and water are required to perform the steam-reforming reaction. The supply amount of water with respect to the supply amount of the material supplied to the reforming section is herein represented by the steam/carbon ratio (hereafter referred to as S/C). For example, in the case that the material is city gas consisting primarily of methane, the S/C is generally required to be approximately 2.5; if the ratio is smaller than that, the steam-reforming reaction cannot be advanced sufficiently, and the amount of hydrogen to be generated is reduced.
If the amount of hydrogen is reduced, a sufficient amount of hydrogen required for a fuel cell cannot be supplied, and the fuel cell cannot generate power. Furthermore, if the S/C to be supplied to the reforming section is reduced, problems occur, a reforming catalyst is degraded, the carbon component contained in the material precipitates, attaches to the reforming catalyst and lowers the performance of the catalyst, and a gas pathway is clogged due to the precipitation of carbon, whereby the pressure loss in the gas pathway increases and a predetermined amount of the material cannot be supplied.
Moreover, the hydrogen-containing gas obtained after the steam-reforming reaction contains approximately 10% of carbon monoxide and the carbon monoxide poisons the anode electrode of the fuel cell; hence, to reduce the concentration of the carbon monoxide, in the hydrogen generating apparatus, a transforming section which performs a transforming reaction is provided subsequent to the reforming section which performs the steam-reforming reaction. The transforming reaction is a reaction in which water and carbon monoxide are transformed into hydrogen and carbon dioxide by the transforming reaction, whereby carbon monoxide is reduced by the reaction.
Still further, if the S/C to be supplied to the hydrogen generating apparatus is reduced, the water to be used for the transforming reaction is also reduced, whereby the carbon monoxide to be reduced by the transforming reaction is also reduced. As a result, the concentration of the carbon monoxide in the hydrogen-containing gas to be supplied to the fuel cell rises, and the anode electrode of the fuel cell is poisoned with the carbon monoxide more significantly.
In the case of a solid polymer fuel cell, it is necessary to reduce the concentration of carbon monoxide to 10 ppm or less, and the hydrogen-containing gas having passed through the transforming section is further subjected to a selective oxidation reaction using oxidative gas, such as air, in a selective oxidation section. Even in this case, if carbon monoxide is not reduced sufficiently in the transforming section, the concentration of the carbon monoxide after the selective oxidation cannot be reduced to 10 ppm or less.
For these reasons, with respect to water which is supplied to the reforming section (hereafter referred to as reforming water), it is necessary to supply a predetermined amount of the water by which the S/C can be maintained appropriately. Hence, an adjustment is made so that the supply amount of the reforming water stably becomes this predetermined amount by providing a flow rate adjusting instrument in a water pathway which supplies the above-mentioned reforming water. (For example, refer to JP-A-2004-6093.)